Capto-dative Substituent Effects in Syntheses with Radicals and Radicophiles [New synthetic methods (32)]

The 100 yers old Wurster's salts have long been recognized as compounds with redical cations. Their unusual stabilization derives partly form capto‐dative (cd) substitution. This principle is now discussed as one factor of radical stabilization and it is applied to simple methine derivatives. cd‐Substitution has synthetically useful applications: cd‐substituents on a carbon atom allow its selective dehydrodimerization. Olefines with geminal and thus cross‐conjugated cd‐substituents are “radicophilic” and permit twofold carbon radical addition. cd‐Substituted olefines are useful antioxidants, polymerization inhibitors and are promising agents in the control of biological radical reactions. Generally, many reactions of cd‐substituted molecules appear to involve radicals. Molecules containing an electron acceptor and an electron donor group are substituted in capto‐dative (cd) manner cd substituents on the same carbon atom stabilize radicals; the stability of Wurster's salts, known for 100 years, is partly due to this effect. Geminally cd substituted olefins are radicophilic.